Wound dressing

ABSTRACT

A wound dressing in the form of a bag enclosing fly maggots, having a porous wall made from plastic, the wall having a membrane made from an open cell polyurethane foam, the pore diameter of which is approximately 0.1 mm to approximately 1 mm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claims priority toPCT/EP2014/064267, filed Jul. 3, 2014, which claims priority to GermanPatent Application No. 10 2013 107 464.2, filed Jul. 15, 2013, theentireties of which are incorporated by reference herein.

BACKGROUND

The application relates to a wound dressing in the form of a bagenclosing fly maggots, having a porous wall made of plastic.

To treat chronic, poor-healing wounds, it is known to insert live flymaggots into the wound. For this purpose, preferably maggots of the blowfly, for example, of the Lucilia sericata, are used. The efficacy of themaggots is based on the wound cleaning (debridement), the anti-microbialactivity and the stimulation of the wound healing. The digestive enzymessecreted by the maggots are substantially responsible for these effects.

The maggots can be inserted into the open wound as so-called freerunners, an adhesive gauze net preventing them from escaping from thewound.

Today, an application of the maggots by way of a bag-shaped wounddressing in which the maggots are enclosed is preferred. The wall of thebag is porous so that the secretion secreted by the maggots can passthrough into the wound and so that the dissolved necrotic tissue canenter the bag and can be taken up by the maggots. Such a wound dressingis known from the publication EP 1 020 197 B1.

In this known wound dressing, the wall is made of a fine-mesh net frompolyamide (for example, nylon fibers) or polyester yarn having meshwidths of approximately 0.12 mm. The use of such wound dressings, which,for example, are marketed under the “BioBag” brand by the companyBiomonde GmbH, Barsbüttel, Germany, is, for example, described in anarticle by G. Cazander et al., “Maggot therapy for wound healing . . .,” Journal of Wound Technology, July 2009, pages 18-23. In order toprevent an adhesive bonding of the walls, a spacer, for example, in theform of a PVA sponge, is preferably inserted into the bag, as a resultof which sufficient room is kept free for the maggots.

In this known wound dressing, the textile net of the wall has to be veryfine-meshed so that the maggots do not widen the mesh and escape. Thisfine-mesh structure has a disadvantageous effect on the porosity of thewall and, for this reason, on the fluid permeability of the wall. Forthis reason, it has been attempted to surround the bag made out of thefine-meshed polyamide net by a polyvinyl alcohol wet membrane. Such awound dressing has been offered under the designation of “VitaPad” bythe above-mentioned Biomonde GmbH. The PVA coating, however, in additionreduces the porosity. PVA foam finds application as a hydro sponge as ahealing-promoting wound dressing. Owing to the strong evaporation, thewater content of the PVA material as a coating can however only preventa drying-out of the maggots in the short-term. For this reason, theentire bandage has to be moistened three times daily to keep the maggotsalive. Moreover, the PVA membrane has to be kept wet because themembrane hardens when drying, no longer conforms to the wound and, asthe case may be, harms the wound edges. The frequent moistening makesthe wound treatment time-consuming. The evaporative cooling lowers thetemperature of the bandage and, for this reason, of the wound, whichnegatively influences the growth of the maggots and the healing of thewound. In particular, the growth of microbial pathogens, so called wetgerms, is promoted by constantly keeping the bandage wet. Infectionscaused hereby represent a dangerous complication of the wound treatment.For this reason, the application of this wound dressing is problematic,for reason of which said wound dressing has meanwhile been withdrawnfrom the market.

SUMMARY

The present disclosure provides a wound dressing which improves theefficacy and safety of the therapy using fly maggots.

The present application provides a wound dressing having the featuresand structures disclosed herein.

Advantageous embodiments and further developments are also disclosedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a wound dressing in the form of abag enclosing live fly maggots according to the present disclosure.

FIG. 2 illustrates a cross-sectional side view of the wound dressing ofFIG. 1 taken along line II-II according to the present disclosure.

FIG. 3 illustrates a cross-sectional side view of another embodiment ofwound dressing according to the present disclosure.

FIG. 4 illustrates another embodiment of a wound dressing with aframe-shaped spacer according to the present disclosure.

FIG. 5 illustrates a cross-sectional side view of the wound dressing ofFIG. 4 taken along line V-V according to the present disclosure.

FIG. 6 illustrates another embodiment of a wound dressing with anadditional inner bag according to the present disclosure.

FIG. 7 illustrates a cross-sectional side view of the wound dressing ofFIG. 6 taken along line VII-VII according to the present disclosure.

FIG. 8 illustrates another embodiment of a wound dressing with anadditional inner bag according to the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In FIGS. 1 and 2, according to the present disclosure, the wounddressing (10) is manufactured in form of a bag enclosing live flymaggots (12), having a wall which is made of a membrane made fromtotally open cell polyurethane foam (PUR foam). Preferably, the opencell structure of the PUR membrane is produced by reticulation. Thetotally consistently open cell structure ensures the fluid permeabilityof the wall of the bag. Preferably, the PUR foam is compressed afterreticulation, as a result of which the stability of the foam material isincreased and the pore size is reduced.

The use of an open cell PUR membrane offers surprising, substantialadvantages vis-à-vis known wound dressings.

Clinical applications have surprisingly shown that it is possible toensure optimal ambient conditions also for the maggots wrapped by thePUR dry membrane, provided that the membrane of the wound dressingdirectly rests on the wound surface. The evaporating surface of the PURmembrane is substantially smaller compared to the PVA wet membrane. Forthis reason, the moisture of the wound secretion in itself mostlysuffices for the survival and growth of the maggots. The care-intensivewetting and wet-keeping of the wound bandage is, therefore, onlyrequired on occasion. The formation of wet germs is largely prevented.

While for wound dressings having a fine-mesh polyamide net a very smallmesh width is necessary to prevent a widening of the mesh openings bythe maggots, the PUR foam does practically not allow for a widening ofthe pore size by the maggots. For this reason, the membrane can bemanufactured having a larger pore diameter and a smaller thickness,improving the permeability of the membrane for the maggot secretion andthe liquefied necrotic tissue.

A further surprising advantage results from that the PUR foam may bemanufactured having a very uniform pore size. For this reason, amembrane can be used, the pore diameter of which is selected at such asize that the maggots are just not able to penetrate into the pores. Themanufacturing and processing technique of the PUR foam enables to reducethe scattering width of the pore size to such an extent that the secureenclosing of the maggots in the bag of the wound dressing is combinablewith an optimal porosity of the membrane.

A further substantial advantage of the PUR membrane is in that this PURmembrane is soft and conforming so that the wound dressing abuts tightlyagainst the surface of the wound, as a result of which the efficacy ofthe maggots and of the maggot secretion is promoted. In this instance,the soft flexural property of the PUR membrane is independent of ambientconditions, that is, particularly also of moisture. For this reason, itis not necessary to monitor and influence the moisture of the wounddressing. In doing so, the application is substantially simplified.

Another embodiment is shown in FIG. 3 where the bag-shaped wounddressing (10) is manufactured from two membrane surfaces (14, 16) placedone upon the other, which are connected to each other at the edges (18),for example, by adhesive bonding or welding. The seams at which theedges are connected with each other stay soft and flexural so that theydo not compromise the abutting of the wound dressing against the woundsurface and so that they do not damage the wound surface. The lowmelting point of PUR particularly enables a welding by simple,cost-effective means and a high reliability.

Owing to the material properties of PUR foam, the walls abutting eachother in the interior of the bag do not have a tendency to adhesivelybond. For this reason, the developing and growing maggots can push thesoft and flexural walls of the bag apart and are not hindered in theirdevelopment without having to additionally insert a spacer into the bag.

The coarse, thin membrane of the PUR foam has a relatively small surfaceso that the fluid evaporation is small. For this reason, there is alower risk that the wound dressing and the enclosed maggots dry out.

The polyurethane foam can be produced based on polyether or polyester.The PUR foam of the membrane has a similarly healing-promoting influenceonto the wound as it is known from PVA dressings. A PUR foam based onpolyether is to be preferred because of its excellent resistance tohydrolysis, its resistance to acids and bases, its excellent flexibilityin low temperatures and, in particular, because of its resistance tomicrobes.

The membrane made of the PUR foam can be manufactured having athickness, that is, a wall thickness, of approximately 0.5 mm or less.Preferably, the thickness of the membrane can be approximately 0.1 mm.This low thickness promotes the soft flexural property of the membraneand the good fluid permeability.

The diameter of the pores of the PUR membrane is selected as great aspossible to ensure a fluid permeability as great as possible on the sideof the wound and a good ventilation of the maggots on the outer side.The upper limit of the pore diameter is determined by the size and, inparticular, the diameter of the maggots. The diameter of the pores ischosen a little smaller than the diameter of the maggots so that themaggots cannot penetrate into the pores, expand the pores and escapethrough the wall.

In the case of the green bottle fly Lucilia sericata, the fly eggs have,for example, an average diameter of 0.47 mm. In the first larval stage,the newly hatched maggots have an average diameter of approximately 0.75mm, a strong variation of +/−50% being observed. In the second larvalstage, the maggots have an average diameter of 1.37 mm, here onlysmaller variations of +/−20% being observed.

It results from these values that the pore diameter of the PUR membraneis to be at least approximately 0.1 mm. A smaller pore diameter wouldonly reduce the fluid permeability; however, it would not have anyadvantage for enclosing the maggots. The upper limit of the porediameter for all potentially considered fly maggots should not exceedapproximately 1.0 mm. Corresponding with the above mentionedmeasurements of the maggots, an upper limit of the pore size diameter ofapproximately 0.4 mm can be used for the maggots of the Lucilia sericataemployed in most cases today. In order to reliably prevent the maggotsfrom penetrating into the pores with their somewhat tapered headsection, a pore diameter of approximately 0.3 mm is preferably chosen.

Another embodiment of a wound dressing is illustrated in FIGS. 4 and 5.To provide sufficient space for the maggots developing in the bag of thewound dressing, a frame-shaped spacer (20) can be inserted in the areaof the interconnected edges of the membrane surfaces (14, 16) formingthe wall of the bag. This spacer (20) increases the clear, innerdistance of the walls; however, it does not reduce the inner surfacearea of the bag.

FIG. 6 and FIG. 7 illustrates another embodiment of a wound dressing. Inthis embodiment, an additional inner bag (22) can be inserted into thebag (10) formed by the PUR membrane. This wall of additional inner bag(22) is also made out of a membrane from open cell PUR foam. The porediameter of the PUR membrane of the inner bag (22) can be ≤0.4 mm. Themembrane of the inner bag (22) has a low tear resistance. As shown inthe embodiment in FIG. 8, the low tear resistance can be achieved inthat the membrane of the inner bag has very thin walls and/orpredetermined breaking lines (24). Such predetermined breaking lines(24) can, for example, be the welding or adhesive bonding seams at theedge of the inner bag.

In this embodiment, the eggs of the fly are inserted into the inner bag(22), which then is wrapped by the outer bag (10). The pore size of theinner bag ensures that the fly eggs cannot slip out of the inner bag(22). Owing to this pore size, the tiny maggots hatching from the eggsalso cannot escape from the inner bag (22). After hatching, the maggotsquickly increase in strength and size so that they produce a highpressure in the inner bag (22) leading to a tearing or bursting of theinner bag (22). Then, the maggots can roam freely in the outer bag (10).In this embodiment, the pore size of the PUR membrane of the outer bag(10) can be chosen corresponding to the size of the maggots escapingfrom the inner bag in the second larval stage. For this reason, the poresize of the wall of the outer bag can, for example, have a diameter ofapproximately 1.0 mm. This embodiment has the advantage that the maggotscan be inserted already as eggs into the wound dressing and can activelycontribute to the healing of the wound already during the earlier firstlarval stage. In the second larval stage, the maggots are then kept inthe outer bag, which can have a considerably larger pore diameter and,therefore, a very high permeability. In this manner, the changingactivity of the maggots during the course of the development of themaggots and the changing composition of the maggot secretion can beoptimally utilized over the entire development duration of the maggots.

What is claimed is:
 1. A wound dressing, comprising: a bag in which flymaggots can be enclosed, the bag having a porous wall made from plastic,wherein the porous wall has a membrane made from a totally open cellpolyurethane foam, the pore diameter of which is approximately 0.1 mm toapproximately 1.0 mm; wherein the bag is an outer bag; and an inner baginserted into the bag, wherein the inner bag has a wall made from openpore polyurethane foam and has a pore diameter of ≤0.4 mm and a low tearresistance.
 2. The wound dressing according to claim 1, wherein the porediameter is ≤0.4 mm.
 3. The wound dressing according to claim 2, whereinthe pore diameter is approximately 0.3 mm.
 4. The wound dressingaccording to claim 1, wherein the membrane has a thickness of ≤0.5 mm.5. The wound dressing according to claim 4, wherein the thickness isapproximately 0.1 mm.
 6. The wound dressing according to claim 1,wherein the polyurethane foam is reticulated.
 7. The wound dressingaccording to claim 1, wherein the polyurethane foam is compressed. 8.The wound dressing according to claim 1, wherein the polyurethane foamis made out of polyether-based polyurethane.
 9. The wound dressingaccording to claim 1, wherein the bag is made of two membrane surfacesplaced one upon the other and connected with each other at an edge ofthe bag.
 10. The wound dressing according to claim 9, further comprisinga frame-shaped spacer located between the membrane surfaces in an areaof the connected edges of the membrane surfaces.
 11. The wound dressingaccording to claim 1, wherein the outer bag has a pore diameter ofapproximately 0.4 mm to approximately 1.0 mm.
 12. A wound dressing,comprising: an outer bag, the outer bag having a porous plastic wall,wherein the porous wall has a totally open cell polyurethane foammembrane with a pore diameter between approximately 0.1 mm toapproximately 1.0 mm; and an inner bag located within the outer bag andin which fly maggots can be enclosed, wherein the inner bag has an openpore polyurethane foam wall with a pore diameter of ≤0.4 mm; wherein theinner bag is configured to rupture after the fly maggots hatch andincrease in size.